The present invention relates generally to image processing, and more specifically to a technique for discriminating between and extracting regions of a document which have been highlighted and regions of a document which have not been highlighted.
Often, it is desirable to differentiate between regions of a document which have been "highlighted" with, for example, a highlight pen from regions of a document which have not been highlighted. By "highlighted" it is intended to mean herein that first marks in a document have been differentiated from remaining marks of the document by a region which has a substantially different gray scale than the background or marks of the original document. Such marks could be made, for example, by way of well known "Hi-Liter" pens, "Major Accent" pens, and other pens which produce bright but relatively transparent colors.
A variety of methods have been proposed for detection of highlighted regions in a document. For example, the use of a color scanner has been proposed to detect regions of a document which have been highlighted in a color different than the remainder of the document. Other processing methods utilize detection of an image which may include shadow, midtone, and bright portions. The midtone portion may be screened with a low frequency screen to convert the image to binary form.
While meeting with some success, prior methods of detecting highlighted regions have met with certain limitations. For example, the use of a color scanner would limit the user to segregation of only original documents or color copies thereof. Further, color scanners are complex and, therefore, expensive. Other methods are not reliable, expensive, slow, or the like in many applications. Some methods fail to detect intended characters which are not fully highlighted and some unintended characters which have been partially highlighted.
From the above it is seen that an improved method and apparatus for detection of highlighted regions of a document is desired.